Dual-tip cantilever

ABSTRACT

A device comprising at least one cantilever comprising at least two tips is described, where the tips have substantially the same tip heights. Methods for making and using such a device are also provided. The height of one tip off of the surface can be more easily determined when the two tips have equal height.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Applications No.61/052,864, filed May 13, 2008, and U.S. Provisional Application No.61/167,853, filed Apr. 8, 2009, each of which are incorporated byreference in their entirety.

BACKGROUND

A need exists to develop better devices and methods to create smallscale structures including microstructures and nanostructures,particularly for commercial operation.

SUMMARY

Provided herein are devices, apparatuses, compositions, methods ofmaking same, and methods of using same.

One embodiment provides a device comprising at least one cantilevercomprising at least two tips, where the cantilever's largest dimensionis about 1000 μm and the tips comprise substantially equal tip heights.In some embodiments, at least one cantilever comprises silicon carbideor silicon nitride. In some embodiments, the tips have substantiallyequal tip heights. In some embodiments, at least one cantilever has aspring constant that is not spatially uniform. In some embodiments, thespring constant of at least one cantilever between two of its tipsdiffers from its spring constant between an attached actuator and thetip closest to the actuator.

Another embodiment provides a device comprising at least one cantilevercomprising at least two tips, where the cantilever's largest dimensionis about 1000 μm and the tips comprise substantially equal tip heights,where the device comprises at least one microscope tip, atomicmicroscope tip, scanning microcope tip, or nanoscope tip.

Yet another embodiment provides a method comprising providing anoxidized silicon wafer with a silicon dioxide layer, patterning thesilicon dioxide layer to form a mask with at least two holes, etchingthe silicon dioxide layer to form two or more pits in the wafer,stripping the silicon dioxide layer, oxidizing the silicon wafer, anddepositing silicon nitride on the wafer to form a cantilever comprisingtwo or more tips. In some embodiments, an e-beam is used for patterning.In some embodiments, the holes are square. In some embodiments, the pitsare pyramidal.

Still another embodiment provides a method comprising providing a devicecomprising an actuator attached to a cantilever comprising two tips,moving the actuator to bring the first tip into contact with a surface,and determining the height of the second tip. In some embodiments, thetwo tips have substantially the same tip height. In some embodiments,the height is determined using the distances of the tips from theactuator. In some embodiments, the height is determined using the ratioof the distances of the tips from the actuator. In some embodiments, theheight is determined using the elevation of the actuator above thesurface.

At least one advantage of at least one embodiment includes improvedheight sensing for a dual tip system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic of a cantilever comprising dual tips withsubstantially equal height.

FIG. 2 provides schematics of a flow chart of a dual-tip cantileverfabrication process.

DETAILED DESCRIPTION

All references cited herein are incorporated by reference in theirentirety.

Introduction

For practice of the various embodiments described herein, lithography,microlithography, and nanolithography instruments, pen arrays, activepens, passive pens, inks, patterning compounds, kits, ink delivery,software, and accessories for direct-write printing and patterning canbe obtained from NanoInk, Inc., Skokie, Ill. Instrumentation includes,for example, the NSCRIPTOR and DPN5000. Software includes, for example,INKCAD software (NanoInk, Chicago, Ill.), providing user interface forlithography design and control. E-Chamber can be used for environmentalcontrol. Dip Pen Nanolithography® and DPN® are trademarks of NanoInk,Inc.

The following patents and co-pending applications related todirect-write printing with use of cantilevers, tips, and patterningcompounds, and related instrumentation, are hereby incorporated byreference in their entirety and can be used in the practice of thevarious embodiments described herein, including inks, patterningcompounds, software, ink delivery devices, and the like:

U.S. Pat. No. 6,635,311 to Mirkin et al., which describes fundamentalaspects of DPN printing including inks, tips, substrates, and otherinstrumentation parameters and patterning methods;

U.S. Pat. No. 6,827,979 to Mirkin et al., which further describesfundamental aspects of DPN printing including software control, etchingprocedures, nanoplotters, and complex and combinatorial array formation.

U.S. patent publication number 2002/0122873 A1 published Sep. 5, 2002(“Nanolithography Methods and Products Produced Therefore and ProducedThereby”), which describes aperture embodiments and driving forceembodiments of DPN printing.

U.S. Pat. No. 7,279,046 to Eby et al. (“Methods and Apparatus forAligning Patterns on a Substrate”), which describes alignment methodsfor DPN printing.

U.S. Pat. No. 7,060,977 to Dupeyrat et al. (“NanolithographicCalibration Methods”), which describes calibration methods for DPNprinting.

U.S. Patent Publication 2003/0068446, published Apr. 10, 2003 to Mirkinet al. (“Protein and Peptide Nanoarrays”), which describes nanoarrays ofproteins and peptides.

U.S. Pat. No. 7,361,310 to Mirkin et al. (“Direct-Write NanolithographicDeposition of Nucleic Acids from Nanoscopic Tips”), which describesnucleic acid.

U.S. Pat. No. 7,273,636 to Mirkin et al. (“Patterning of Solid StateFeatures by Direct-Write Nanolithographic Printing”), which describesreactive patterning and sol gel inks (now published Aug. 28, 2003 as2003/0162004).

U.S. Pat. Nos. 6,642,129 and 6,867,443 to Liu et al. (“Parallel,Individually Addressable Probes for Nanolithography”), describing activepen arrays.

U.S. Patent Publication 2003/0007242, published Jan. 9, 2003 to Schwartz(“Enhanced Scanning Probe Microscope and Nanolithographic Methods UsingSame”).

U.S. Patent Publication 2003/0005755, published Jan. 9, 2003 to Schwartz(“Enhanced Scanning Probe Microscope”).

U.S. Pat. No. 7,093,056 to Demers et al., describing catalystnanostructures and carbon nanotube applications.

U.S. Pat. No. 7,199,305 to Cruchon-Dupeyrat et al., and U.S. Pat. No.7,102,656 to Mirkin et al., describing printing of proteins andconducting polymers respectively.

U.S. Pat. No. 7,005,378 to Crocker et al., describing conductivematerials as patterning compounds.

U.S. patent application Ser. No. 10/689,547 filed Oct. 21, 2003, nowpublished as 2004/0175631 on Sep. 9, 2004, describing mask applicationsincluding photomask repair.

U.S. Pat. No. 7,034,854 Cruchon-Dupeyrat et al., describingmicrofluidics and ink delivery.

U.S. patent application Ser. No. 10/788,414 filed Mar. 1, 2004, nowpublished as 2005/0009206 on Jan. 13, 2005 describing printing ofpeptides and proteins.

U.S. Pat. No. 7,326,380 to Mirkin et al., describing ROMP methods andcombinatorial arrays.

U.S. Pat. No. 7,491,422 to Zhang et al., describing stamp tip or polymercoated tip applications.

U.S. patent application Ser. No. 11/065,694 filed Feb. 25, 2005, nowpublished as 2005/0235869 on Oct. 27, 2005, describing tiplesscantilevers and flat panel display applications.

US Patent publication 2006/001,4001 published Jan. 19, 2006 describingetching of nanostructures made by DPN methods.

WO 2004/105046 to Liu & Mirkin published Dec. 2, 2004 describes scanningprobes for contact printing.

US patent application “Active Pen Nanolithography,” Ser. No. 11/268,740to Shile et al. filed Nov. 8, 2005 describes for examplethermcompression bonding and silicon handle wafers.

DPN methods are also described in Ginger et al., “The Evolution ofDip-Pen Nanolithography,” Angew. Chem. Int. Ed. 2004, 43, 30-45,including description of high-throughput parallel methods. See alsoSalaita et al., “Applications of Dip-Pen Nanolithography,” NatureNanotechnology, 2007, Advanced On-line publication (11 pages).

Direct write methods, including DPN printing and pattern transfermethods, are described in for example Direct-Write Technologies,Sensors, Electronics, and Integrated Power Sources, Pique and Chrisey(Eds), 2002.

The direct-write nanolithography instruments and methods describedherein are of particular interest for use in preparing bioarrays,nanoarrays, and microarrays based on peptides, proteins, nucleic acids,DNA, RNA, viruses, biomolecules, and the like. See, for example, U.S.Pat. No. 6,787,313 for mass fabrication of chips and libraries; U.S.Pat. No. 5,443,791 for automated molecular biology laboratory withpipette tips; U.S. Pat. No. 5,981,733 for apparatus for the automatedsynthesis of molecular arrays in pharmaceutical applications.Combinatorial arrays can be prepared. See also, for example, U.S. Pat.Nos. 7,008,769; 6,573,369; and 6,998,228 to Henderson et al.

Scanning probe microscopy is reviewed in Bottomley, Anal. Chem., 1998,70, 425R-475R. Also, scanning probe microscopes are known in the artincluding probe exchange mechanisms as described in, for example, U.S.Pat. No. 5,705,814 (Digital Instruments).

Microfabrication methods are described in for example Madou,Fundamentals of Microfabrication, 2^(nd) Ed., 2002, and also Van Zant,Microchip Fabrication, 5^(th) Ed., 2004.

See for example U.S. Pat. No. 6,827,979 to Mirkin et al. is alsoincorporated by reference in its entirety.

US Patent Publication 2003/0022470 and Publication 2006/0228873 to Liuet al. describe cantilever fabrication methods.

US Patent Publication 2006/0040057 to King, Sheehan et al. describesthermal DPN printing methods.

U.S. Provisional Applications No. 61/052,864, filed May 13, 2008, andU.S. Provisional Application No. 61/167,853, filed Apr. 8, 2009, arealso both incorporated by reference in their entireties.

Companion US applications “Piezoresistor Height-Sensing Cantilever” and“Heated Cantilever”, both filed May 13, 2009 as Ser. No. ______ and Ser.No. ______ respectively, are both incorporated by reference in theirentireties.

Cantilevers

Some embodiments comprise devices comprising one or more cantilevers.Some cantilevers may be of microscopic dimension. Some cantilevers maybe of nanoscopic dimension. Some cantilevers may be used in such devicesas atomic microscopes, scanning microscopes, or nanoscopes. Somecantilevers may be used to deposit materials on surfaces, measure localheights of surfaces, and the like.

In some embodiments, cantilevers may comprise silicon nitride.Alternatively, they may comprise silicon carbide. These materials aretough polycrystalline ceramics, having high wear resistances. Bothsilicon nitride and silicon carbide are electrical insulators.Cantilevers made from these materials can show different propertiescompared to silicon cantilevers. Because these materials are alsochemically inert, cantilevers made from them may also be used withbiological materials. Silicon nitride may be more readily commerciallyavailable than silicon carbide.

Some cantilevers may be configured into arrays. Such arrays may beone-dimensional. Some arrays may have more than one dimension. In someembodiments, cantilevers are configured into two-dimensional arrays.

Tips

Some cantilevers may comprise two or more tips. Some tips may comprisethe same materials as the rest of their cantilevers. In someembodiments, tips may comprise different materials than the rest oftheir cantilevers.

Some tips may extend below the rest of their cantilevers. Such tips maycontact a surface below their cantilevers. Some tips may take upsubstances from surfaces or deposit substances to surfaces.

Some tips may be scanning tips. Scanning can be done over the X-Y planeof a surface, and tips can be used to image or deposit materials. Suchtips may be used to detect features of surfaces or substances onsurfaces below their cantilevers. Such features may include localphysical dimensions such as height, local chemical compositions, and thelike.

Some tips may be microscope tips, such as atomic microscope tips. Sometips may be nanoscopic tips. Other variants will be understood by thoseskilled in the art.

Some embodiments comprise cantilevers with two or more tips havingsubstantially equal tip heights. A tip may be characterized by its tipheight, which refers to the distance from the point of the tip to thebase of the tip, measured perpendicularly to the cantilever. Two tipheights are said to be substantially equal if the shorter tip height isno less than about 90% of the longer tip height, preferably no less thanabout 95% of the longer tip height, and more preferably no less thanabout 99% of the longer tip height. Two or more tip heights are said tobe substantially equal if each of the tip heights is substantially equalto the longest tip height.

Sensing Height

Two fundamental activities associated with cantilevers are positioningtips over specific locations on a surface and determining the verticaldisplacements (heights) of the tips with respect to the surface. Bothactivities can involve knowledge of positions of the tips relative tothe actuators that direct the cantilevers' movements.

A dual tip cantilever can have a proximal tip and a distal tip. Herein,one can know the height of a proximal tip relative to the surface when adistal tip is touching, while using the existing z-height sensingequipment of an instrument like an AFM.

One source of uncertainty is the fact that materials expand and contractin response to changes in temperature. Materials' responses arecharacterized by their coefficients of thermal expansion, which maydiffer according to composition. Where different materials are used, forexample in cantilevers and their tips, this uncertainty is compounded.

In some embodiments, it is possible to determine the vertical height oftips above a surface. For example, consider embodiments comprising acantilever with two or more tips having substantially equal tip heights.In such cases, geometry can be used to determine the actual verticalheights of each the tips above a surface. For example, FIG. 1 depicts adual-tip cantilever attached to a z-piezo actuator located a distanceZ_(o) above a surface. One of the two tips is just contacting thesurface. In such a case, the distance of the second pen is given by:

$\begin{matrix}{Z_{2} = {Z_{0}\left( {1 - \frac{L_{2}}{L_{1}}} \right)}} & (1)\end{matrix}$

where L₁ and L₂ are the horizontal displacements of the respective tippoints from the actuator. Note that the effects of thermal expansion orcontraction do not affect this relationship, provided the materials ofthe tips are identical, because the lengths L₁ and L₂ appear as a ratioin Equation 1. This principle can be extended to three or more tips in asimilar manner.

This method may be used in conjunction with tip tracking methods, suchas those based on strain gauges, laser fluorometry and the like.

Fabricating Cantilever and Tips

In preparing the cantilever, one embodiment provides a cantilevercomprising two or more tips, wherein the cantilever is prepared by: (i)providing an oxidized silicon wafer comprising a silicon dioxide layeron silicon, (ii) patterning the silicon dioxide layer to generate etchopenings adapted for formation of at least two tips per cantilever,(iii) etching the silicon wafer anisotropically, (iv) depositing andpatterning silicon nitride to form the cantilever, and (v) optionallybonding the cantilever to a handle wafer.

Fabrication of the pen can be carried out with adapted process flowsdeveloped by Quate's group during the 1990's (1,2). In one embodiment,this process starts with a highly accurate e-beam written mask topattern two or more square openings onto an oxidized silicon surface,which will become two or more tips. The openings can be of any size. Forexample, they can be between about 1 micron to about 60 microns, such asbetween about 2 microns to about 50 microns. The size of the two or moreopenings can be the same or different from one another.

Subsequently, the wafer can be immersed in a KOH etch solution to etchanisotropically pyramidal pits into the silicon wafer to form the basictip mold(s). The masking oxide can then be stripped and the wafersre-oxidized at 950° C. for 360 minutes to grow about 3900 Å of siliconoxide. At this time and temperature, the oxide at the bottom of the pitis hindered with respect to growth, and thus when a cast film isdeposited in this pit, the tip sharpness can approach a 10 nm tip radiusor smaller. No maximum limit of the tip size need to be imposed. Forinstance, the tip size can be increased by increasing the pit size.

Silicon nitride with low stress gradient can then be deposited onto themold wafer to form a cantilever. In one embodiment, the nitridethickness is about 600 nm. Accordingly, with this thickness and a widthof 25 um and a length of 200 um, a rectangular cantilever in thisembodiment can have a spring constant of about 0.04 N/m. While this is avalue that is commonly used for contact mode AFM probes and can workwell for DPN, other spring constants may also be obtained and used. Notto be bound by any particular theory, the spring constant changeslinearly with width w and with the third power of length L such that fora given thickness t, a wide range of spring constants K can be obtained:K=Ewt³/4L³, where E will depend on the materials of construction. In onealternative embodiment, the thickness of the nitride may also be changedon a batch basis to have a larger variation in spring constant. Forexample, nitride thicknesses from 400 nm to 1000 nm for cantilevers(with spring constant ranging from 0.0015 to over 1 N/m) have been usedby Nanolnk for different applications.

In some embodiments, the spring constant may vary from one location toanother along the cantilever. Such variation in spring constants may beeffected by using different cantilever widths or thicknesses at thedifferent locations. For cantilevers with two tips, some embodimentsprovide a spring constant between the tips that differs from the springconstant between the actuator and the tip nearest the actuator.

The nitride can be oxidized, patterned, and etched to form thecantilevers. See FIG. 2. See also, (1) T. R. Albrecht, S. Akamine, T. E.Carver, and C. F. Quate, “Microfabrication of cantilever styli for theatomic force microscope,” J. Vac. Sci. Technol. A, Vac. Surf. Films(USA), 1990; (2) S. Akamine, and C. F. Quate, “Low temperature oxidationsharpening of microcast tips,” J. Vac. Sci. Technol B., vol. 10, No. 5,September/October 1992.

Non-Limiting Working Example #1

1) Starting material

2) Clean 3) Oxidation 4) Clean

5) Tip lithography

6) Descum 7) Oxide Etch 8) Strip Resist/Clean 9) Tip Etch 10) Clean 11)Strip Oxide 12) Clean 13) Oxidize 14) Sharpen Lithography 15) Inspect16) Oxide Etch 17) Strip Resist/Clean 18) Deposit Silicon Nitride 19)Cantilever Lithography

20) Frontside etch

21) Backside Lithography 22) Backside Etch 23) Strip Resist/Clean 24)Actuator Lithography 25) Descum 26) Clean 27) Etch Non-Limiting WorkingExample #2

The procedure of Example #1 was repeated, with the following changes:(1) Steps 14-17 were not used, and (2) prior to Step 18, wet oxidationwas performed.

1. A device comprising at least one cantilever comprising at least twotips, said at least one cantilever further comprising a length, a width,and a thickness, and said at least two tips comprising at least two tipheights, wherein the largest of said length, said width, and saidthickness is less than about 1000 μm, and wherein said at least two tipheights are substantially equal.
 2. The device according to claim 1,wherein said at least one cantilever comprises silicon nitride orsilicon carbide.
 3. (canceled)
 4. The device according to claim 1,wherein the at least one cantilever is one of an array of cantilevers.5-9. (canceled)
 10. The device according to claim 1, wherein at leasttwo tips are atomic force microscope tips.
 11. The device according toclaim 1, wherein at least one tip is a nanoscopic tip.
 12. The deviceaccording to claim 1, wherein said at least one cantilever comprises twotips.
 13. The device according to claim 1, wherein said at least two tipheights comprise a longest tip height, wherein said at least two tipheights are no less than about 95% of said longest tip height. 14.(canceled)
 15. The device according to claim 1, wherein said at leastone cantilever is attached to an actuator, said at least one cantileverfurther comprising a first tip and a second tip, said at least onecantilever further comprising a first spring constant between saidactuator and said first tip and a second spring constant between saidfirst tip and said second tip, wherein said first spring constant andsaid second spring constant are not the same.
 16. A device comprising acantilever comprising a first tip and a second tip, said cantileverfurther comprising a length, a width, and a thickness, said first tipcomprising a first tip height, and said second tip comprising a secondtip height, wherein the largest of said length, said width, and saidthickness is less than about 1000 μm, and wherein said first tip heightand said second tip height are substantially equal.
 17. A methodcomprising: (i) providing a first oxidized silicon wafer comprising afirst silicon dioxide layer and a silicon substrate, wherein said firstsilicon dioxide layer is disposed on said silicon substrate, (ii)patterning said silicon dioxide layer with a mask to form a maskedsilicon dioxide layer, said mask comprising a first two or moreopenings, (iii) etching said masked silicon dioxide layer to form asecond two or more openings in said masked silicon dioxide layer and toform two or more pits in said silicon substrate, (iv) stripping saidmasked silicon dioxide layer, (v) oxidizing said silicon substrate toform a mold wafer, (vi) depositing silicon nitride onto said mold waferto form a cantilever comprising two or more tips in the pits. 18.(canceled)
 19. The method according to claim 17, wherein said first twoor more openings are square. 20.-22. (canceled)
 23. The method accordingto claim 17, wherein said first two or more openings comprise at leasttwo lengths and at least two widths, wherein said at least two lengthsare substantially equal and wherein said at least two widths aresubstantially equal.
 24. (canceled)
 25. The method according to claim17, wherein said etching is anisotropic.
 26. The method according toclaim 17, wherein said two or more pits are pyramidal. 27-28. (canceled)29. A method comprising: (i) providing a device and a surface, saiddevice comprising an actuator attached to a cantilever, wherein saidcantilever comprises a first tip and a second tip, (ii) moving saidactuator to contact said first tip with said surface. (iii) determiningheight of said second tip above said surface, wherein said first tipcomprises a first tip height and said second tip comprises a second tipheight, wherein said first tip height and said second tip height aresubstantially equal.
 30. The method according to claim 29, wherein saidheight of said second tip is determined using a first distance from saidactuator to said first tip and a second distance from said actuator tosaid second tip.
 31. The method according to claim 29, wherein saidheight of said second tip is determined using a ratio of a firstdistance from said actuator to said second tip to a second distance fromsaid actuator to said first tip.
 32. The method according to claim 29,wherein said height of said second tip is determined using an elevationof said actuator above said surface, a first distance from said actuatorto said first tip, and a second distance from said actuator to saidsecond tip.
 33. The method according to claim 29, wherein said height ofsaid second tip is determined using an elevation of such actuator abovesaid surface and a ratio of a first distance from said actuator to saidsecond tip to a second distance from said actuator to said first tip.34. The method according to claim 29, wherein said height of said secondtip Z₂ is determined using an elevation of such actuator above saidsurface Z_(o), a first distance from said actuator to said first tip L₁,and a second distance from said actuator to said second tip L₂ accordingto the formula:$Z_{2} = {{Z_{0}\left( {1 - \frac{L_{2}}{L_{1}}} \right)}.}$